Cooling systems for cooling beverages or other fluids to a desired temperature typically circulate the beverage through lines (or coils) immersed in water or other liquid which is kept at a freezing temperature. A compressor or other cooling means is employed which circulates refrigerant through cooling coils also immersed in the water or other liquid in order to cause ice formation around the cooling coils. Thus, the liquid phase of the water or other liquid is maintained at the freezing temperature in equilibrium with the solid phase. The frozen liquid around the coils is referred to as an ice bank. As heat is transferred from the beverage to the water or other liquid, the ice surrounding the cooling coils melts. The ice bank thus serves as a heat sink for cooling the beverage. The water remains at a freezing temperature, however, as long there is still sufficient ice present. The heat transferred from the beverage is absorbed as the latent heat of melting, leaving the temperature of the water unchanged. The compressor and circulating refrigerant must, however, cause new ice to be formed in place of the melted ice if the system is to operate continuously. It is therefore necessary to have a closed-loop control system which senses the amount of ice surrounding the cooling coils and actuates the compressor appropriately.
Devices for controlling the size of an ice bank in such cooling systems, ice bank control devices", utilize ice sensing means positioned at a certain distance from the cooling means so that the operation of the cooling means can be controlled relative to that distance. Since the liquid usually crystallizes progressively and radially outward from the cooling coils while the cooling system is cooling the liquid, ice bank control devices therefore allow the ice bank to grow to a predetermined size at which point the cooling cycle of the cooling means is interrupted by the ice bank control device.
Conventional ice bank control devices have generally been of the mechanical type. These devices commonly use a capillary tube containing a solution which freezes when the tube is surrounded by ice. The expanding frozen solution within the capillary tube then compresses a diaphragm which operates an electrical switch. The electrical switch serves to turn a cooling compressor on or off and, thereby, controls the extent of ice formation.
More modern ice bank control devices, however, utilize electronic sensing means to determine the presence of ice. In such devices, electrodes are immersed in the water and current is fed from one electrode to another which is held at ground potential. If a constant current source is used, the potential of the first electrode will be proportional to the resistance of the water or other medium present. Thus, detection of the presence of ice is enabled since the electrical resistance of a liquid changes (usually to a greater resistance) when it undergoes a phase transformation into the solid form. When such a sensing method is combined with a suitable controller, the result is a closed-loop feedback control system which causes the cooling means (typically comprising a compressor) to operate often enough to maintain the water at its freezing point but not so often that excessive ice is formed.
Such electronic ice bank control devices present a number of advantages over their mechanical counterparts including lower cost and greater reliability. Because the electrical resistance of solid phase water is much higher than that of liquid water, such monitoring has enabled fairly accurate determination of the presence of ice. Also, since electronic devices measure the phase change directly rather than indirectly by measuring temperature, their operation is not effected by changes in the freezing point of the water caused by the addition of solids.
Since the cooling means of a system employing such an electronic ice bank control either operates or is shut off, the control scheme is usually referred to as an "on-off" or a "bang-bang" controller. With such systems, the resistance of the water surrounding the cooling coils is compared with a reference value and, if there is a difference, an error signal is produced which causes the compressor to shut off. In the prior art, the reference value is ordinarily a fixed, standard value believed to correspond to that of liquid water.
The resistance of the water used to produce the error signal (hereinafter called "variable resistance") is monitored at a predetermined position a certain distance from the cooling coils. When the value of the variable resistance rises at that position above the reference value, the previous methods indicate that ice has formed at the predetermined position, and this indication initiates the interruption of the cooling process.
A fundamental characteristic of all on-off controllers is oscillation of the controlled variable about the set point. Since the actuator of such a system is operated in an on-off fashion, environmental influences will cause the controlled variable to deviate from the set point when the actuator is off. This produces an error signal to turn the actuator on until the error signal is reduced to zero, and the cycle repeats. Such cycling is normal but is undesirable, if it is too rapid, particularly if the actuator is a mechanical device such as a compressor Rapid start-stop cycles ("fast-cycling") cause excessive wear to the compressor as well as inefficient use of energy. A well known technique of solving this problem is to incorporate a "dead-band" into the controller. A "dead-band" is a range about which the controlled variable is allowed to deviate from the set point before the actuator is either activated or turned off. This is accomplished by making the set point of the system vary between two values according to whether the actuator is on or off. Thus, when the controlled variable is between the higher or lower set points, there is no change in the previously derived error signal which causes the actuator to either remain on or off. Therefore, the range between the higher and lower set points is effectively a "dead-band". In water cooling applications, precise control relative to the controlled variable is not necessary since the only objective of the control scheme is to prevent excessive ice formation around the cooling coils. Incorporating a dead-band into the system, therefore, involves no significant disadvantages.
The most basic of previous similar methods for controlling water cooling involves, simply, measuring the electrical resistance between a single probe and a grounded reference. Circuitry or other means are connected to the probe in order to measure this resistance and compare it with a predetermined fixed value of resistance, which value has been previously determined as a standard for water. A fundamental problem with such a method utilizing a single resistance reading is that there is no means for providing a dead-band. Lack of a dead-band causes the aforementioned practical problems the compressor may undergo rapid start-stop cycles ("fast-cycling") when the progression of ice is immediately adjacent the probe. To solve this problem of fast-cycling, a dead-band must be incorporated into the control system by either mechanical or electronic means.
Another previous method involves monitoring resistance sensors from two probes. The utilization of two probes in this latter method effectively provides for a dead-band. A dead-band is achieved by electronically requiring that both probes sense the ice in order to stop the compressor while also requiring that the ice melt off both probes in order to activate the compressor once again. A predetermined value for the resistance of water has invariably been used as a reference value for this and each other of the previous methods. This previous method involves positioning a first of the two probes nearer the cooling coils so that it will ordinarily sense the progression of ice before the second probe and will sense melting after the second probe. The dead-band, therefore, occurs when the first probe senses the ice and when the ice melts from around the second probe. When the system is in this state, the compressor will remain in this previous operating mode, either on or off. If the total volume of the ice pack surrounding the cooling coils is viewed as the controlled variable, this system will cause that variable to oscillate between two set points, represented by ice surrounding the first and both probes, respectively.
Unfortunately, since each of the previous inventions depends on a fixed, predetermined value for the resistance of liquid water, the resulting indications are not always accurate since extraneous and nonstandard factors affect the resistance readings within any tank of water, particularly after extended usage. Most basically, the resistance of water may vary in different geographical locations due to local impurities in the water, which impurities generally raise the resistance of water. Resistance of the liquid water may similarly change within a system over time due to evaporation of the water, which evaporation raises the amount of impurities per volume of water remaining.
Increased resistance of liquid water is also caused by increased amounts of impurities within the system due to accumulation over time. Employment of similar methods also creates problems in systems where the impurity content or the identity of the liquid is purposefully altered; in such situations the reference value must be changed, thus causing delays, particularly when circuitry must be accordingly modified.
Furthermore, deposits on submerged electrical probes, which deposits are natural over time, often affect the resistance measurements. The additional resistance of deposited impurities adds to the resistance which the probe reads, thereby raising the apparent resistance of the water. With the passage of time, coatings of such impurities inevitably adhere to virtually any probe which is submerged in liquid water that is the slightest bit impure. Notably, these coatings tend to be of uniform thickness on surfaces that are subjected to similar environments. Electrolytical plating on the probes may also affect the apparent resistance of the water as recorded by such probes. The electrolytical type deposits have been minimized with some previous methods by utilizing an alternating current rather than a direct current; however, in practice, slight electrolytical plating still occurs with an alternating current. Electrical probes necessary with every employment of the art, therefore, must be periodically replaced or cleaned when incorporated for use with previous inventions.
Therefore, it is a primary object of the present invention to provide an apparatus and method which accounts for resistance variances of water as well as apparent variances in this resistance caused by impurities deposited on the electrical probes, while providing a method for indicating the phase transformation of liquid water to ice.
It is also an object of the present invention to measure the apparent resistance of the liquid. This measured, apparent resistance can be used as a reference rather than some fixed or predetermined value. Changes in the composition of the water will then be automatically compensated for. It is also an object to compensate for changes in the probes themselves. Deposits, electroplating or other factors.
Another object of the present invention is to provide a means for mounting the aforementioned probes for use in an ice bank control system. The mounting of the probes (or "electrodes") must be such that the ground electrode and the reference electrode must always be immersed in liquid water. The two ice sensing electrodes or probes must be mounted so as to define the space in which the ice bank is allowed to grow by the control system.
It is a further object of the present inventions to enable adjustment of the size of the ice bank according to varying operating conditions. For example, if there are to be periods of heavy use, it would be desirable to raise the heat capacity of the heat sink. By increasing the size of the ice bank, the cooling system can handle more throughput of beverage without lowering the temperature of the water bath. Also, different sizes and configurations of the vessel containing the water bath and the associated cooling coils may dictate different optimal sizes of the ice bank. It would be desirable, therefore, for the electrode mounting means to allow a user to adjust the size of the ice bank to suit each individual application.
A related object is to provide detecting means in the form of a plurality of probes with means for mounting onto the coils of a cooling system which forms an ice bank, wherein the mounting means has features which advantageously correlate and provide for adjustment of the positions of the probes.
Another object of the present invention is to provide electrodes and mounting means for use in an ice bank control system of the type described above which render the electrodes relatively resistant to mechanical damage when the cooling coils are lowered into the water bath or removed therefrom. During such operations, there is always the possibility that the electrodes will contact the sides of the water bath vessel or the beverage coils. It is desirable, therefore, to minimize the possibility of breaking or deforming the electrodes as their location is critical to the operation of the ice bank control system. For example, to demonstrate the critically of the probe positions, if the reference electrode were to be broken off or bent during installation of the cooling coils so as to be located closer to the cooling coils than the ice sensing electrodes, the control system would never shut off the compressor and the entire water bath would freeze as a result. The entire cooling system could thereby be completely destroyed.
It is a still further object of the present invention to provide a means allowing the electrodes to be readily replaced with a minimum effort. As aforementioned, electroplating is inevitable in any control system of this type. When the resulting deposits on the electrodes become severe enough to warrant replacement of the electrodes, any time expended during the replacement operation by a repairman is expensive. Also, the time for which the entire system must be shut down may cause expense to a user of the cooling system. It is desirable, therefore, for any electrode mounting means to allow the electrodes to be removed and replaced with a minimum of time and effort.
Furthermore, previous methods have utilized a grounded electrical reference that is dependent on the system in which the previous method is employed. This presents a particular problem where the method is employed in a container or system that is insulated. It is, therefore, another object of the present invention to incorporate the use of a round probe which is independent from the system in which the method is employed.
It is another object of the present inventions to effectively minimize electrolytical plating and coating of electrical probes utilized with the invention.
It is also an object of the present invention to provide an apparatus which utilizes and enables the methods of the present invention.
Another object of the present invention is to provide an apparatus for detecting whether material at a certain location is distinguished from material at a second location, particularly by determining differences in the electrical resistances at the two locations. Yet another object of the present invention is to provide means for detecting the presence or absence of a solid phase in a liquid phase, which means includes protective features for ensuring the desired operation thereof.
Additionally, it is an object of the present invention to provide a method for sensing the presence of a solid phase of any material within a liquid phase of any material, including but not limited to water.
It is another object of the present invention to avoid fast-cycling of apparatus related to any particular employment of the present invention by providing for a dead-band.
Additionally, with the advent of electronic ice bank control devices, there has developed a need for a specialized packaging and connecting apparatus. It is, therefore another object of the present invention to provide a housing for the electronic control circuitry which will serve to protect the electronic components and electrically conductive surfaces from contact with water.
It is a further object of the present inventions to provide a means for easily removing and replacing a printed circuit board upon which the elements of the electronic control circuit are mounted. As all electronic components are destined to fail at some time or other, it is desirable that removal and replacement be accomplished with a minimum of time and effort in order to lower service costs. Much time and effort can be saved by minimizing the number of electrical and mechanical connections which must be severed before the electronic control circuitry can be removed. Accordingly, it is an object of the present invention to provide a connecting means for the printed circuit board containing the electronic circuitry which allows the removal of the printed circuit board without affecting power or sensor connections.
It is still a further object of the present invention to provide a means integral to the housing which allows the state of the final control output of the electronic circuitry to be observed. The final control output is invariably a contact closure, and it is desirable for the state of the contact to be observable without removing the housing or using a voltmeter at the output terminals. For example, when servicing the entire cooling apparatus, it is necessary to determine if the electronic control circuitry is operating properly independent of the operation of the compressor.